III-V compounds are frequently adopted in the manufacturing of light-emitting diodes (LEDs). Among the III-V compounds, gallium nitride (GaN)-based materials, featuring advantages of direct bandgap, wide bandgap, high-strength chemical bonding and good anti-radiation strength, are extensively developed and thus prevail in blue/green to ultraviolet light-emitting elements as well as high-power and high-temperature electronic elements in the recent years.
Currently, as large-sized GaN wafers cannot be fabricated, most GaN semiconductors need to employ a substrate having a substantial amount of lattice mismatch as GaN. Due to the strain caused by lattice mismatch between a substrate and epitaxial thin-films, misfit dislocation is often generated. Further, a stereotypic optoelectronic element is usually a heterostructure, in which strain energy are easily accumulated on the heterojunction due to lattice mismatch and thermal expansion coefficient difference between epitaxial layers. The strain energy often causes misfit dislocation during processes of manufacturing and utilizing elements. The misfit dislocation defects usually generate and begin from a heterojunction, and become traps or recombination centers for minority carriers at active regions of the element to degrade characteristics and quality of such semiconductor elements. For example, in an LED, the existence of dislocation defects causes excess carriers not to release energy in form of radiative recombination, such that the light-emitting efficiency of the LED is undesirably affected.
Due to the lack of a substrate having a lattice constant that completely matches GaN, GaN thin-films are mostly grown by heteroepitaxial growth. Taking a most prevalent aluminum oxide substrate for example, physical and chemical properties of the aluminum oxide substrate are quite stable. However, lattice mismatch between the aluminum oxide substrate and a GaN thin-film is approximately 16%, which results in a high defect density of the GaN thin-film on the aluminum oxide substrate. To effectively reduce a dislocation density, many methods have been raised by researchers and developers for solving the problem. The epitaxial lateral over growth (ELOG) technique is a common method for solving the above problem. For example, the EP publication No. 1054442, “Method for Growing Epitaxial Group III Nitride Compound Semiconductors on Silicon”, discloses a method for growing aluminum gallium nitride on a silicon substrate by using the ELOG technique for mitigating the issue of misfit dislocation.
Lithography and etching processes are required during the growth of GaN using the ELOG method, and so different manufacturing machines are involved in the overall manufacturing process. Thus, not only the overall manufacturing process is complicated, but also a yield rate is reduced owing to environmental factors among different machines to further cause increased production costs.